A flat foot in the adult may occur as a new problem i.e. the shape of the foot changes from one which was otherwise normal to one which is now flat, or the feet have always been flat and only recently become symptomatic. In either case, the problem usually arises as a result of stretching or tearing of a tendon called the posterior tibial tendon, which is the major dynamic support the arch of the foot. Once this tendon stretches out, the arch will sag, and unfortunately, the deformity gets progressively worse over time unless treated. Usually the initial treatment is to support of the arch including an orthotic or a brace. This will be an effective treatment in approximately 70% of patients. In those patients where an orthotic does not work many eventually require surgery to reconstruct the arch of the foot. There are many different operations that are used, but wherever possible, every effort should be made to preserve the movement of the foot and avoid a fusion of affected joints.